The Multi-Finger Caliper (40 finger) is a multi-arm mechanical contact logging instrument used to detect the internal conditions of the casing in oil and gas wells. It can be regarded as a precise mechanical hand that "touches" the casing downhole.
Application Fields
It is mainly used for engineering inspection of casing. The core application fields include:
Casing Damage Detection- Identify casing deformations (such as ellipticity, diameter reduction, diameter expansion), bending and wrinkles.
Corrosion & Wear Evaluation-Detect corrosion pits, holes and uniform wear on the inner wall of the casing.
Perforation Hole Quality Inspection-Evaluate the shape and position of the holes after perforation operations to determine if there are burrs or excessive deformations.
Casing Collar locator–Accurately measures and positions every casing collar and its inner diameter.
Operation Effect Evaluation-Used to assess the changes in casing conditions before and after downhole operations such as cement squeezing, casing scraping, and salvage.
How to Measure & Evaluate Wellbore Integrity?
The core of wellbore integrity is to ensure that the casing (with the cement ring as its external support) can effectively seal the formation and withstand various mechanical and chemical loads. The Multi-Finger Caliper (40 finger) directly measures and indirectly evaluates it in the following ways:
1. Directly Measure the Mechanical Integrity of the Casing
Estimation of Wall Thickness Loss
The remaining wall thickness of the casing can be indirectly estimated by precisely measuring the change in the inner diameter. If the original outer diameter and wall thickness of the casing are known, an abnormal increase in the inner diameter usually indicates corrosion or wear, while an abnormal decrease in the inner diameter indicates scaling or deformation.
Precise Defect Location
It offer an extremely high circumferential coverage density, enabling precise depiction of the location and geometric dimensions of defects such as corrosion and pits. This is crucial for assessing the severity of the defects and formulating repair plans.
2. Identify Potential Risk Points
Risk of seal failure
Severe deformation or corrosion perforation of the casing can damage the pressure seal of the wellbore, leading to interlayer flow or wellhead pressure. The 40-arm data can clearly identify these high-risk areas.
Risk of structural failure
Large section diameter reduction or severe bending of the casing can affect the insertion and setting of subsequent downhole tools (such as packers and bridge plugs), and may even lead to the casing being crushed or broken. The 40-arm data is a key input for evaluating the remaining structural strength of the casing.
Integrity of the Perforation Zone
Inspect the cracks or deformations around the perforation holes to determine whether they will affect the fracturing or production effect.
3. Provide decision-Making Basis for Well Repair & Abandonment Operations
Locating of Casing-Patch Setting Depth
Before inserting the subsidized casing into the damaged section of the casing, it is necessary to precisely understand the length and inner diameter of the damaged section to ensure that the subsidized casing can pass smoothly and be effectively set.
Guide the Cement Extrusion Operation
Judge whether cement is being lost through casing splits or perforation tunnels.
Abandonment Design
For permanent plug-and-abandonment, verifies that the casing at the intended bridge-plug depth is sound to ensure long-term isolation integrity.
Conclusion
The Multi-Finger Caliper (40 finger) is a key diagnostic tool for ensuring the integrity of oil and gas well shafts and safe production. Unlike acoustic logging that reflects the quality of cement bonding (such as eight-sector instruments), it focuses on the mechanical state of the casing itself.
◆ The core advantage lies in its ability to provide high-resolution and high-precision circumferential change information of the inner diameter of the casing, visually presenting the health status of the casing in a graphical way, and achieving precise diagnosis from "whether it is intact" to "where and how it is damaged".
◆ The limitation lies in that it mainly reflects the condition of the inner wall of the casing and is powerless against the corrosion and cement ring conditions on the outside of the casing. Usually, it needs to be combined with other logging methods such as electromagnetic thickness gauges to make a more comprehensive evaluation of wellbore integrity.
In conclusion, it serves as the "eye" for inspection, maintenance and repair operations within the casing in the middle and later stages of oilfield development. It plays an irreplaceable role in extending the lifespan of oil Wells, preventing safety accidents and protecting the environment.
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